This invention relates to an improved method for copolymerizing THF and an alkylene oxide or cyclic acetal. It is more particularly directed to such a method carried out in a reaction medium which contains an acylium ion precursor and a polymeric catalyst which contains .alpha.-fluoro sulfonic acid groups.
Copolyether glycols, i.e., polyethers made by copolymerizing alkylene oxides or cyclic acetals with tetrahydrofuran (THF), and having terminal hydroxyl groups, are known and are useful in the manufacture of polyurethanes. These glycols can be prepared by copolymerizing THF and alkylene oxides, using as a catalyst a polymer of ethylenically unsaturated monomers containing .alpha.-fluoro sulfonic acid groups, as shown in copending application Ser. No. 868,112, filed Jan. 9, 1978.
While that process is satisfactory, it tends to proceed rather more slowly than is usually desired. It has now been found that the rate of such a copolymerization can be significantly increased if the polymerization reaction mass contains an acylium ion precursor. This improved process yields ester end-capped copolyether glycol, which can be converted to copolyether glycol by alcoholysis.